My current staking is now running 14 days. 99.75% stake in 24 hours and 4.07% stake in 10 minutes. Those percentages are going up rather slowly. I hope I stake before any of these major changes take affect.

I am interested will the difficult also be affected by reduction? Or our sprouts ammount will be reduced and difficult stay the same? Or there will be another reward system at all?

I can only estimate an answer to this, but the difficulty in staking would remain the same it is today if the number of wallets staking remains the same (so, if the number of wallets that are staking shrinks, then the difficulty will go down, and vice versa).

As far as I know the only change to the reward system will only be to reduce the percentage anyone receives from a stake. This is meant to reduce the total inflation rate for the coin in general from around 200% to 500% (annualized) that it is today, to a more reasonable smaller number.

As I understand since today’s information about Sprouts+. It means the new currency at all. So we just exchange Sprouts to Sprouts+ so that is how the reward will be changed and the difficulty will be different at all.
But this is just my assumption.